Electrical heating elements



United States Patent [72] Inventor Everett F. Kelrn Corning, New York [21] Appl. No. 723,164 [22] Filed April 22, 1968 [45] Patented Oct. 20, 1970 [73] Assignee Corning Glass Works Corning, New York a corporation of New York [54] ELECTRICAL HEATING ELEMENTS 3 Claims, SDrawing Figs.

[52] US. Cl. 140/715, 29/61 '1 [51] Int.Cl B2lf 1/04, 1105b 3/00 [50] FieldofSearch 140/71, 71.5, 7l.6,92.l,105;29/61l [56] References Cited UNITED STATES PATENTS 761,204 5/1904 Carpenter 29/61 1 1,013,572 1/1912 Suman 140/921 FOREIGN PATENTS 596,485 1/1948 Great Britain 140/715 Primary Examiner-Lowell A. Larson Attorneys-Clarence R. Patty, Jr. and Charles W. Gregg ABSTRACT: A method of bending electrical resistance wire to form electrical heating elements for heating substantially rectangular areas of electrical heating units or surfaces. The wire is first bent into a strip of undulated or sinuate wire comprising a first succession of similar undulations or curved sections of relatively small radii with successive ones of the undulations being alternately on opposite sides of a centerline for said strip and a second succession of similar undulations or curved sections between each successive pair of undulations of said first succession with successive ones of each undulation of each such second succession being alternately on opposite sides of said centerline. The undulations of the second successions thereof are located a distance from said centerline a distance less than the undulations of said first succession. Each undulation of said first succession is then rebent in the direction opposite to that in which it was previously bent to form the strip of undulated or sinuate wire into a succession of short strip lengths extending parallel with one another alternately in opposite directions to provide heating elements for said areas of the heating units or surfaces.

Patented Oct. 20, 1970 Z; i 54 I 1}, mm 4o 34 3434 Fig. 5 34 Evereff Ix): iEA;;R/.m ela/baa W AGENT ELECTRICAL HEATING ELEMENTS BACKGROUND OF THE INVENTION Machines for bending wire into sinutate, serpentine or undulated strips of wire of indefinite length are known. However, it is often desired to use strips of undulated or sinuously or serpentinely bent electrical resistance wire for forming heating elements for generally rectangular areas of electrical heating units or surfaces and it has been found that when the radii of curvature of the undulations or curved sections of the bent resistance wire are relatively short, such as being equal to the diameter of the resistance wire for example, the strips of previously bent resistance wire cannot, without causing the undulations of the wire to touch other undulations thereof, be rebent to form generally rectangular areal patterns of short strip lengths. It is, therefore, an object of the present invention to provide a method for bending electrical resistance wire into a strip of selectively undulated wire comprising undulations of relatively small radii of curvature and then selectively rebending such strip of undulated wire into a pattern of short strips of undulated wire for use in heating generally rectangular areas of electrical heating units or surfaces, such rebending of the strip of undulated wire being performed without any undulations thereof touching other undulations of the strip or strips.

SUMMARY OF THE INVENTION In practicing the invention and accomplishing the abovementioned object thereof, electrical resistance wire is bent into a sinuous or serpentine wire strip comprising a succession of curved sections or undulations extending alternately first equal distances on opposite sides of a centerline for said wire strip and with a second succession of similar undulations recurring singly at regular intervals along said strip, each successive undulation of such second succession extending alternately second equal distances on opposite sides of said centerline, such second equal distances being greater than said first equal distances. Said wire strip is then rebent at each undulation of said second succession thereof to form a rectangular undulated pattern of short length undulated strips.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will best be understood with reference to the drawings wherein:

FIG. 1 comprises a view of a strip of undulated or sinuate wire in which the undulations or curved sections thereof have relatively large radii of curvature;

FIG. 2 comprises a view illustrating the manner in which strips of wire bent as in FIG. 1 can be rebent to form generally rectangular patterns of wire for generally rectangular areas;

FIG. 3 comprises a view similar to FIG. 1 but in which the radii of curvature of the undulations or curved sections of the undulated wire have relatively small radii of curvature;

FIG. 4 comprises a view similar to FIG. 2 but illustrating the rebending of a strip of wire, bent as in FIG. 3, to form a generally rectangular .pattern of wire;

FIG. 5 is a view similar to FIG. 3 but illustrating a strip of wire bent in accordance with a first step of the present invention;

FIG. 6 is a view similar to FIG. 4 and illustrating the manner in which strips of wire bent as in FIG. 5 are preferably rebent, in accordance with a second step of the invention, to form generally rectangular patterns of wire for generally rectangular areas;

FIG. 7 is a view similar to FIG. 6 and illustrating the manner in which strips of wire bent as in FIG. 5 can be alternatively rebent, in accordance with the second step of the invention, to form generally rectangular patterns of wire for generally rectangular areas; and

FIG. 8 is a view illustrating the preferable manner of rebending a strip of wire such as shown in FIG. 5, in accordance with said second step of the invention, to form a generally rectangular pattern of wire for a generally rectangular area.

Similar reference characters refer to similar parts in each of the views of the drawings.

PREFERRED EMBODIMENT OF THE INVENTION Referring to the drawings in detail there is shown in FIG. 1 a length of wire 10 which has been sinuously or serpentinely bent into a strip 11 of undulated wire comprising a sucession of undulations, curves or curved sections such as 12 having large radii of curvature relative to the diameter of the wire. Successive undulations or curves 12 of said succession thereof extend equally and alternately in opposite directions on opposite sides of a centerline 13 for undulated strip 11.

As illustrated in FIG. 2, a strip such as 11 of wire such as 10 can readily be rebent as at curve or undulation 14 of such wire strip to form said strip into a generally rectangular configuration or pattern comprising a plurality of short strips 15 of said wire. It will be noted that the rebending of wire whose undulations or curves have large radii of curvature relative to the diameter of the wire can be readily performed, as illustrated in FIG. 2, without the wire touching itself at the centers of the curves or undulations of the wire. Therefore, when the wire, such as 10, of a strip of wire, such as 11, is electrical resistance wire which is formed as illustrated in FIG. 2 into an electrical heating element having a generally rectangular pattern and intended to be disposed in or against a generally rectangular area of an electrical heating unit or surface, no probiems arise because the strip of wire 111 (FIG. I) can be rebent as illustrated in FIG. 2 to form said heating element with relatively large spaces such as 16 provided between the undulations or curves of wire I0 which are adjacent each other as a result of the rebending of the wire and, therefore, no causes for short circuits at such spaced points in the heating element result from such rebending.

It is, however, usually desirable to provide electrical heating elements in which the electrical resistance wire is sinuously or serpentinely bent to form a strip of undulated wire in which the straight sections between the undulations or curves are disposed relatively close to each other for the purpose of obtaining the maximum heat possible per unit of area of said heating element. A strip 21 of electrical resistance wire 20 is illustrated in FIG. 3 as being so bent. It will be noted that the undulations or curves such as 22 of the strip of wire 21 have small radii of curvature relative to the diameter of wire 20. As shown in FIG. 3 the inner radii of curvature of the undulations or curves 22 of wire strip 21 are approximately about equal to the diameter of wire 20 of such strip. In all other respects the strip of wire 21 is similar to strip 11 of FIG. 1, each successive undulation or curve such as 22 extending alternately equidistantly on opposite sides of a centerline 23 for strip 21.

As illustrated in FIG. 4, in the rebending of a strip, such as 21, of wire, such as 20, as at the center of a curve or undulation, such as 22a thereof, and for the purpose of forming the strip of wire 21 into a plurality of short strips such as 25 and which are similar to strips 15 of FIG. 2, the curves or undulations of wire 20 which are adjacent each other as a result of the rebending of the wire will contact each other, as at points such as 26 shown in FIG. 4, due to the previously mentioned small radii of curvature of such curves or undulations.

Referring now to FIG. 5 of the drawings, there is shown an undulated strip 31 of electrical resistance wire 30 which is initially bent, in accordance with a first step of the present invention, similar to strip 21 of FIG. 3 but including a modification in the series of undulations provided in wire strip 31 during the initial bending of wire 30 to form such strip. Such modification in the series of undulations provided in wire strip 31 in accordance with the first step of the invention comprises the bending of wire 30 into a strip of undulated wire 31 including a first succession of similar undulations or curves, such as 34, of relatively small radii of curvature with successive ones of such undulations or curves extending alternately a first selected distance on opposite sides of a centerline 33 for wire strip 31, and a second succession of similar undulations or curves, such as 340, between the undulations of each successive pair of undulations of said first succession thereof but with successive ones of each undulation of each said second succession extending alternately a second selected distance,

less than said first selected distance, on opposite sides of said centerline for strip 31. In other words, the first step of the invention comprises bending a length of wire 30 into a sinuate or serpentine strip of wire 31 having a series of similar successions of an even number of similar and nearly semicircular first curved sections of wire, such as 340, of relatively small radii of curvature, with each such curved section of each succession being connected with each next curved section of the respective succession by relatively straight sections of wire such as 30a, and said curved sections being spaced alternately at preselected equal distances from opposite sides of centerline 33 for said strip of wire. The strip of wire 31 further includes, between each of said series of similar successions of first curved sections of wire, a second curved section of wire such as 34 with each such second curved section preferably having a radius identical to those of said first curved sections of wire 34a by relatively straight sections of wire. The even number of first curved sections of wire in each of said series of successions thereof is preferably selected in accordance with the size and configuration of an area, such as a selected rectangular area of an electrical heating unit or surface, in or against which it is intended that an electrical heating element formed of wire 30 be disposed. However, as illustrated in FIG. 5, the strip of wire 31, having eight undulations or curves in each succession of said series of successions of first curved sections of wire, can be suitably rebent, as further described hereinafter, to correspond to many rectangular areas of different sizes and configurations.

As illustrated in FIG. 7, the strip of wire 30 (FIG. 5) may be rebent, in accordance with the second step of the invention, at the center of each said second curved section 34 of wire 31, similar to the rebending of wire strip 21 as illustrated in FIG. 4. Such rebending can be performed with suitable spaces 36 (similar to spaces 16 illustrated in FIG. 2) being provided between the undulations or curves of wire 30 which are adjacent each other as a result of the rebending of such wire. However, because most electrical resistance wire is subject to rapid fatigue and possible resultant breakage from repeated bending thereof at any one point therealong, it is preferably to rebend wire strip 31 adjacent each curve, undulation or curved section 34 of wire 30 in the manner illustrated in FIG. 6, rather than substantially at the center of each such curved section as illustrated in FIG. 7. It is intended, however, that the phrase adjacent the center, as used herein in connection with the centers of the undulations, curves or curved sections such as 34, is to be considered to apply to the rebending of the wire such as 30 in either of the manners illustrated in FIGS. 6 and 7 although, as mentioned above, the preferably manner of rebending the wire is that shown in FIG. 6.

FIG. 8 illustrates the rebending of the strip of wire 31 of FIG. 5, in the manner illustrated in FIG. 6, to form such strip of undulated, sinuate or serpentine wire into a succession of short strip lengths, such as 35, extending parallel with one another in opposite directions in accordance with the second step of the invention. The strip of wire 31 of FIG. 5 is illustrated in FIG. 8 as being rebent to generally correspond to a rectangular area such as shown by broken line 40 in FIG. 8 surrounding the rebent strip of wire. It will, however, be apparent to those skilled in the art that a strip of wire such as 31 but of indefinite length can be rebent, as illustrated in FIGS. 6 and/or 7, in various patterns conforming to rectangular areas of many different sizes and configurations as previously mentioned. When, of course, the length of the wire strip such as 31 is longer than needed for a particular rectangular area, the excess wire strip can be cut from either or both ends of the rebent wire strip following the rebending of the wire in accordance with the second step of the invention. As also previously mentioned, the undulations, curves or curved sections of wire such as 34 can be periodically provided along a strip of wire such as 31 in any repetitive sequence and, therefore, when it is desired to bend wire such as 30 into an electrical heating element for a heating unit or surface having an area of an odd or peculiar configuration in or against which it is desired to dispose such heating element, a strip of wire similar to 31 and having curved sections such as 34 in a correct sequence for rebending of the strip to correspond to said odd or peculiar shaped area can be readily formed to provide the desired heating element.

Although there is herein shown and described in detail only one example of the practice of the inventive method disclosed, it will be understood that such is not intended to be considered in any way limiting but that the protection sought for the invention is intended to be limited only by the spirit and scope of the appended claims.

Iclaim:

1. The method of forming electrical heating elements from electrical resistance wire and to be used for heating a generally rectangular area of a heating unit or surface, such method comprising:

A. bending said wire into a strip of undulated wire comprising a first succession of similar undulations having maximum inner radii of curvature approximately equal to the diameter of said wire, successive ones of such undulations extending alternately a first selected distance on opposite sides of a centerline for said strip, anda second succession of similar undulations between the undulations of each successive pair of undulations of said first succession thereof, successive ones of each undulation of each such second succession extending alternately a second selected distance, less than said first selected distance, on opposite sides of said centerline and such undulations having radii of curvature similar to those of said first succession thereof; and

B. rebending said wire, adjacent the center of each said undulation of said first succession thereof and in the direction opposite to that in which such wire was previously bent to form the respective undulation, to form said strip of undulated wire into a succession of short undulated strip lengths extending parallel with one another alternately in opposite directions.

2. The method in accordance with cla m 1 and in which the undulations of each said second succession thereof are even in number, such number being chosen in accordance with the shape of said rectangular area of said heating unit.

3. The method of forming electrical resistance wire into a heating element for a heating unit having an area of a generally rectangular configuration to be heated, such method comprising:

A. bending said wire into a strip of sinuate or serpentine wire comprising a series of similar successions of an even number of similar and nearly semicircular first curved sections of wire each having a maximum inner radius of curvature approximately equal to the diameter of said wire and each such curved section being connected with each next curved section of each said succession by relatively straight sections of said wire and successive curved sections of each said succession being spaced alternately at preselected equal distances from opposite sides of a centerline for said strip of wire, and such strip further comprising, between each of said series of successions of first curved sections of wire, a second curved section of said wire, each such second curved section being spaced a selected distance, greater than said preselected distance, from said centerline of said strip, each such second curved section of wire preferably having a radius identical to those of said first curved sections of wire and being connected with its adjacent curved sections of wire by relatively straight sections thereof, and the number of said first curved sections of wire in each of said series of successions of wire being selected in accordance with the size and configuration of said area of said heating unit; and

B. rebending said wire, adjacent'the center of each said second curved section thereof and in the direction opposite to that in which such wire was previously bent to form the respective curved section, to form said strip of strip lengths having a pattern conforming in configuration to said area of said heating unit. 

